Communicable Diseases

• What is a pathogen?


  A microorganism that causes disease to a host organism, causing damage through directly damaging tissue or through releasing toxins.
• What are examples of pathogens?


  Bacteria, viruses, fungi, parasites.
• What is bacteria?


  These are single celled and prokaryotic microorganisms that exist in an array of environments, eg. soil, water, and the human body.
• What are the two categories of bacteria?

  Gram-positive and Gram-negative.
• How can we tell if bacteria is gram positive or negative?


  Prokaryotic cells can be determined by their shape and cell wall structure, and we can determine the chemical and physical properties of the cell wall using gram staining.
• What are the properties of gram positive and negative bacteria?


  Thick layers of peptidoglycan in the cell walls of positive and very little in the cell walls of negative.
• What is peptidoglycan?


  A polymer that makes up the cell wall of bacteria, consisting of carbohydrate and protein subunits.
• What stain determines gram positive bacteria?


  Crystal violet.
• What stain determines gram negative bacteria?


  Safranin.
• How can we carry out staining?


  Crystal violet is first added and then safranin, if the bacteria retains a purple stain it is positive, but if it retains a pink stain it is negative.
• Why is the bacteria type important?


  The cell wall and therefore type of bacteria determines how it will respond to antibiotics.
• What are the shapes of bacteria?


  Cocci, bacilli, vibrio, spirilla.
• What is cocci (spherical) bacteria?

  This bacteria have less surface area to volume ratio than others, and can therefore survive in drier environments, eg. causes acne.
• What is bacilli (rod) bacteria?

  Have greater surface area to volume ratio, allowing them to more effectively trace up nutrients from dilute substances, eg. causing food poisoning.
• What is vibrio (curved) bacteria?


  Have greater surface area to volume ratio, allowing them to more effectively trace up nutrients from dilute substances eg. causing cholera.
• What is spirilla (spiral) bacteria?

  Their spiral shape allow them to move in a corkscrew motion and meet less resistance from the substance they are moving through, eg. causing stomach alcers.
• How does bacteria cause disease?


  They produce toxins and cause symptoms through cell damage, damaging the cell membranes, enzymes, or genetic material.
• How does bacteria reproduce?

  Binary fission - the process by which a single organisms splits into two genetically identical daughter cells, a type of asexual reproduction found in prokaryotes, and a few single celled eukaryotes.
• What is involved in binary fission?


  • DNA replication - the organisms DNA is duplicated.
  • Cell growth - the cell membrane and cytoplasm extends, preparing the cell for division.
  • Segregation - DNA copies attach to different parts of the cell membrane, moving to opposite ends of the cell.
  • Cytokinesis - the cell membrane pinches inwards, splitting the cell into two daughter cells, each with its own set of DNA.
• What is a virus?


  A non living, acellular (one cell), infectious agent, that replicates inside the living cells of its host organism.
• What does a virus consist of?


  It consists of genetic material (DNA and RNA), a capsid (protein shell), and attachment proteins, and is also smaller in size than bacteria.
• How does a virus cause disease?


  Through penetration of a host cell, where they will then use the host to replicate and spread, causing damage to tissues and triggering immune responses.
• How does the virus replicate?


  • Attachment - a virus attaches itself to a specific receptor on the surface of a host cell, with each virus having specific receptors it can bind to, which is why some virus are species specific.
  • Entry - Once attached it will penetrate the cell, either by merging its membrane with the cell membrane or by being engulfed into the cell, releasing viral genetic material into the host cell.
• How does the virus replicate?


  • Replication - Virus uses host cell machinery to replicated and produce viral proteins, disrupting normal cell function, as resources that should be used in maintaining cell functioning are used in virus reproduction.
  • Assembly and release - new virus particles are assembled from replicated genetic material and proteins and the newly formed viruses exit the cell, often causing it to burst (lysis) or budding out of the cell membrane (an outgrowth), spreading to other cells.
• What is a retrovirus?


  A type of RNA virus that uses the enzyme reverse transcriptase to transcribe its RNA genome into DNA and integrate it into the host cell's genome, using single stranded RNA as its genetic material.
• What is a genome?


  A genome is the complete set of genetic material (DNA or RNA) present in an organism.
• How does a retrovirus work?

  • Attachment - binds to specific receptors on the skin, fusing with cell membrane and releasing its RNA and enzymes into the cell.
  • Reverse transcription - the viral enzyme reverse transcriptase uses RNA as a template to convert the RNA into single stranded DNA, and DNA polymerase enzyme makes double stranded DNA from this.
  • Integration - the newly created viral DNA is transported into the cell's nucleus and is inserted into the host's DNA with the help of the integrase enzyme, with the integrated DNA being called provirus, and remains in the cell's genome permanently.
• How does a retrovirus work?


  • Transcription and translation - the host cell's machinery reads the proviral DNA and produces viral RNA and proteins.
  • Assembly and release - viral RNA and proteins assemble into new virus particles within the host cell, particles that bud off from the host cell, acquiring a portion of its membrane to form a viral envelope.
  • Spread and infection - new virus particles infect other cells, repeating the cycle.
• What is a fungi?


  This is a eukaryotic organism with a membrane bound nuclei, and can be both multi or single celled, eg. yeast and mushrooms.
• How does fungi cause disease?


  Pathogen fungi are parasitic, releasing enzymes that digest host tissues.
• What is a protoctista?


  These are eukaryotes that exist as single celled organisms or cells grouped in colonies, very few being pathogenic, eg. amoeba and plasmodium.
• How do protoctista cause disease?


  They are parasites, living on or in the host at the expense of said host , causing dangerous symptoms, and being transmitted via a vector.
• What is non infectious diseases?


  These are diseases caused by lifestyle, genes, or working conditions, eg. a chronic illness.
• What are infectious diseases?


  Diseases caused by pathogenic microorganisms that can be transmitted from one person to another.
• What are the main modes of transmission of infectious diseases?


  • Hot temperatures - increased heat provides kinetic energy for chemical reactions and reproduction.
  • Social factors - poverty results in poor infrastructure, a lack of fresh food and water, poor sanitation, and overcrowded living quarters, as well as a lack of readily available vaccines and medicines.
• What are increasing factors of disease?

  • A compromised immune system.
  • Socioeconomic factors.
  • Poor nutrition.
  • Overcrowding.
  • Climate change.
  • Poor waste disposal.
  • Poor infrastructure.
  • Culture.
• What is communicable and non communicable disease?


  Communicable - spreads from person to person. Non-communicable - does not spread from person to person.
• How can communicable disease be directly transmitted?


  • direct contact - transferring of bodily fluids, skin to skin contact, and microbes from faeces.
  • inoculation - break in the skin, sharing of needles, and animal bite.
  • ingestion - taking in contaminated food or liquid, transferring pathogen from the hand to mouth.
• How can communicable disease be indirectly transmitted?

  • fomites - materials or objects carrying infections.
  • droplets - saliva and mucus expelled when talking or sneezing and coughing.
  • vectors - transmit disease from host to host, eg. mosquitoes transmit malaria and rats fleas transmit the bubonic plague.
• What are the primary defences of the body?

  • Substances on skin
  • Expulsive reflexes
  • Saliva in mouth
  • Hair and mucus in nostrils
  • Tears from eyes
  • Wax in ears
  • Clotting of blood
  • Acid in stomach
  • Bacteria in gut
  • Urine excretion
  • Menstrual cycle
  • Faeces excretion